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Questions and Answers Regarding Health Concerns and Potential Shortage of
Nelfinavir (marketed as Viracept)
Viracept was recently recalled from the European market due to unacceptably high levels of an impurity known as ethyl methanesulfonate (EMS). EMS is an impurity created during the Viracept manufacturing process. The manufacturing and distributing company for Europe is Roche, whereas Pfizer manufactures and markets Viracept in the United States.
As a consequence of the recall in Europe, Pfizer tested its drug supply of Viracept. Most of the testing has shown EMS levels within final acceptable limits. The FDA and Pfizer have agreed to temporary limits of exposure of this impurity to allow for continued use in populations where the benefits of taking Viracept outweigh potential risks. The manufacturing process is being refined to ensure that EMS levels meet final acceptable limits.
The FDA will update this document as new information becomes available.
1. What is Viracept?
Viracept is an antiretroviral medicine for HIV. It is taken in combination with other anti-HIV medications. It is approved for use in adults and in children older than 2 years of age who are infected with human immunodeficiency virus (HIV-1), the virus that causes acquired immune deficiency syndrome (AIDS). Most adults who take Viracept take the 625mg tablet. Children may be prescribed the 250mg tablet or the powder formulation.
The active substance in Viracept, nelfinavir mesylate, is a protease inhibitor. It blocks an enzyme (protease) necessary for the reproduction of HIV-1. When the enzyme is blocked, the virus does not reproduce normally, slowing down the spread of infection.
2. What is known about the impurity ethyl methanesulfonate (EMS)?
Ethyl methanesulfonate (EMS), also known as ethyl mesylate, is carcinogenic (causes cancer), mutagenic (harmful to DNA, the genetic material in cells) and teratogenic (harmful to a fetus) in animals. It is considered a possible carcinogen in humans. The level at which EMS may become carcinogenic to humans is not known. During the manufacturing process of Viracept, EMS may be formed as an impurity. However, manufacturing steps can be taken to minimize the chances of EMS formation. FDA and Pfizer have taken steps to test and limit the amount of EMS allowed in Viracept.
3. What are the consequences for patients who are taking Viracept now?
Based on the investigation conducted by Pfizer, some patients taking Viracept may have been exposed to EMS levels higher than specified acceptable limits. Available information about genotoxicity, carcinogenicity and teratogenicity of EMS comes from animal studies. No human data is currently available. The level of risk to patients who have been exposed to EMS is therefore difficult to measure. However, children and pregnant women who are receiving Viracept are considered to be at higher risk from exposure to higher levels of EMS. Viracept is not approved for children younger than 2 years of age.
4. Why is Viracept not being recalled in the United States?
The levels of EMS detected in Pfizer-manufactured Viracept are lower than the levels of EMS detected in Roche-manufactured Viracept that triggered the recall in Europe. At this time, FDA and Pfizer consider the risks of unintended interruption of HIV treatment that may result from a recall to be greater than the risks associated with taking Pfizer-manufactured Viracept. Also taken into consideration in this decision is the fact that other HIV antiretroviral medications that patients are switched to may be carcinogenic, mutagenic or teratogenic in animal studies.
5. What should patients do next?
Patients who are currently receiving Viracept should contact their doctor immediately to discuss whether they should continue to take Viracept and to discuss treatment plans in the event of a drug shortage (discussed further below). As a precaution, pregnant women who are receiving Viracept should be switched to alternative anti-retroviral therapy unless no alternative therapy is available for them.
6. What should healthcare providers do next?
Pfizer has provided a Dear Healthcare Provider letter for more information. The text of the letter will be available at FDA’s MedWatch website at http://www.fda.gov/medwatch/index.html.
Healthcare providers should prescribe alternative anti-retroviral therapy to pregnant women currently receiving nelfinavir unless no alternative therapy is available for them.
7. Will there be a shortage of Viracept?
The Food and Drug Administration (FDA) and Pfizer are working together to minimize the risk of a drug shortage. Acceptable limits for the presence of EMS have been set in order to allow for continuing use in populations where the benefit of using Viracept outweighs the risk. However, patients and providers should be aware that a temporary interruption of drug supply may occur and be prepared to start alternative treatments in case changes to antiretroviral medicines are needed.
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Date created: September 10, 2007
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